1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to providing a content service, and more particularly, to a method and apparatus for providing a content service, in which a subscriber, who uses the content service, decrypts encrypted contents using a plurality of pieces of decryption information, and is provided with the contents during a period of using the content service to which the subscriber subscribes.
2. Description of the Related Art
In general, a broadcast service is not transmitted directly to a specified receiver, that is, through “one to one” transmission, but the broadcast service is transmitted to N unspecified receivers, that is, through “one to N” transmission. A system has been used, such that a broadcast service subscriber (hereinafter, simply referred to as a “subscriber”), who has valid viewing authority to view the broadcasted contents, can only receive predetermined broadcast contents, and each digital broadcasting receiver determines whether the subscriber can receive the predetermined broadcast contents or not.
FIG. 1 is a conceptual diagram of how a broadcast service is provided according to the related art.
A broadcast service provider desires to only provide a broadcast service to a subscriber who has viewing authority to view contents of the broadcast service from the broadcast service provider, and the subscriber desires to receive the broadcast service during a period the subscriber desires.
To this end, an encryption system implemented by the broadcast service according to the related art includes a master key Km processing unit, a work key Kw processing unit, and a scramble key Ks processing unit. The scramble key Ks is used as a key that encrypts broadcast contents, and the work key Kw is generated so as to correspond to a period during which the subscriber uses the broadcast service according to a contract made between the subscriber and the broadcast service provider. Further, the master key Km is a unique key for each subscriber.
First, a process in a transmitter side 2 that provides the broadcast service will be described. The subscriber 1 communicates with the transmitter side 2 using an authentication protocol. When the authentication is successfully completed, the subscriber 1 acquires the master key Km from the transmitter side 2. The acquired master key Km is unique to each subscriber, and is stored in a predetermined storage area of a receiver side 4 that receives the broadcast service. Further, at this time, a work key Kw and a scramble key Ks are transmitted together to the subscriber.
In the next process, the transmitter side 2 encrypts the broadcast contents using the scramble key Ks, and the scramble key Ks is encrypted using the work key Kw. Further, the work key Kw and contract information of the subscriber 1 are encrypted using the master key Km, and transmitted to the receiver side 4.
Since the receiver side 4 has already received and stored the master key Km, the work key Kw, and the scramble key Ks from the transmitter side 2, the receiver side 4 performs decryption in reverse order from the order in which the broadcast contents have been encrypted at the transmitter side 2. That is, when receiving the encrypted broadcast contents, the receiver side 4 decrypts the work key Kw and the contract information using the stored master key Km, and decrypts the scramble key Ks using the stored work key Kw. Further, the receiver side 4 decrypts the encrypted broadcast contents using the scramble key Ks and accesses the broadcast contents.
However, according to the related art, when the broadcast service provider provides different periods during which the respective subscribers 1 use the broadcast service, the existing subscribers 1 need to update the keys (e.g., work key Kw) related to the broadcast service whenever another subscriber 1 makes a new contract with the broadcast service provider. Therefore, problems, such as the complexity of managing and maintaining the keys, and a corresponding increase in data exchange between the transmitter side 2 and the receiver side 4, are caused. The problems will be described in more detail with reference to FIG. 2.
FIG. 2 is a conceptual diagram of key distribution when a broadcast service is provided according to the related art.
As described above, the broadcast service provider encrypts the broadcast contents and only provides the encrypted broadcast contents to the authorized subscriber. Then, the subscriber decrypts the provided broadcast contents using the master key Km, the work key Kw, and the scramble key Ks, which are received when the subscriber makes a contract with the broadcast service provider on the broadcast service, and uses the decrypted broadcast contents.
For example, as shown in FIG. 2, a first subscriber C1 makes a contract with a broadcast service provider and desires to use a broadcast service during a first use period 12. Likewise, a second subscriber C2 makes a contract with the broadcast service provider and desires to use the broadcast service during a second use period 14, and a third subscriber C3 makes a contract with the broadcast service provider and desires to use the broadcast service during a third use period 16. The broadcast service provider makes the contract with the first subscriber on the broadcast service, encrypts a work key Kw, which is generated so as to correspond to the first use period 12, using a master key Km of the first subscriber, and provides the encrypted work key Kw. In addition, when the broadcast service provider makes the contract with the second subscriber on the broadcast service, the broadcast service provider encrypts a work key Kw, which is generated to correspond to the second use period 14, using a master key Km of the second subscriber, and provides the encrypted work key Kw. Thereafter, the broadcast contents are encrypted 11 every time unit 10 during the period of using the broadcast service, and transmitted to the subscribers. At this time, the scramble key Ks needs to be continuously updated every several seconds, and the work key Kw needs to be updated whenever a new subscriber subscribes to the broadcast service. As a result, as the number of subscribers increases, the number of keys that need to be distributed, maintained, and managed is also increased.
Further, when the broadcast contents are encrypted and provided to a receiver, the encrypted contents are decrypted by the receiver using the master key Km, the work key Kw, and the scramble key Ks of each of the subscribers. The decrypted broadcast contents are then provided to each of the subscribers of the broadcast service.
Meanwhile, when the subscribers C1 and C3 are provided with the broadcast service in the same broadcast service time unit 18, if the subscriber C3 cancels the contract on the broadcast service and secedes from the broadcast service, the broadcast service provider updates the keys of the subscriber C1. The broadcast service provider then provides the broadcast service such that the subscriber C3, who has seceded from the broadcast service, is not provided with the broadcast service any more. As such, according to the related art, when another existing subscriber secedes from the broadcast service or a new subscriber subscribes to the broadcast service so as to receive the broadcast service, the existing subscribers need to update the decryption keys in their possession, which causes inconvenience to the existing users.
Therefore, the complex distribution, management, and maintenance of the keys according to the related art in order to provide the broadcast service needs to be improved, and the broadcast service needs to be provided to a subscriber in a more efficient manner.